chore: rename project Roundtable → Steward

Renames the Python package directory, CLI command, env var prefix,
docker-compose service/container/image, Postgres role/db, and all
visible branding. Marketing form is "Fabled Steward".

Clean break from the previous rebrand: drops the fabledscryer→roundtable
import shim in __init__.py and the FABLEDSCRYER_* env var fallback in
config.py and migrations/env.py. Env vars are now STEWARD_* only.

Heads-up for existing deployments:
- Postgres user/db renamed fabledscryer → steward in docker-compose.yml.
  Existing volumes need the role/db renamed inside Postgres, or override
  POSTGRES_USER/POSTGRES_DB to keep the old names.
- Host-agent systemd unit is now steward-agent.service. Existing agents
  keep running under the old name; reinstall to switch.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

steward/models/hosts.py

@@ -0,0 +1,29 @@
+from __future__ import annotations
+import enum
+import uuid
+from datetime import datetime, timezone
+from sqlalchemy import Boolean, DateTime, Enum, Integer, String
+from sqlalchemy.orm import Mapped, mapped_column
+from .base import Base
+
+
+class ProbeType(str, enum.Enum):
+    tcp = "tcp"
+    icmp = "icmp"
+
+
+class Host(Base):
+    __tablename__ = "hosts"
+
+    id: Mapped[str] = mapped_column(String(36), primary_key=True, default=lambda: str(uuid.uuid4()))
+    name: Mapped[str] = mapped_column(String(128), nullable=False)
+    address: Mapped[str] = mapped_column(String(255), nullable=False)
+    probe_type: Mapped[ProbeType] = mapped_column(Enum(ProbeType), nullable=False, default=ProbeType.tcp)
+    probe_port: Mapped[int] = mapped_column(Integer, nullable=False, default=80)
+    ping_enabled: Mapped[bool] = mapped_column(Boolean, nullable=False, default=True)
+    dns_enabled: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False)
+    dns_expected_ip: Mapped[str | None] = mapped_column(String(255), nullable=True)
+    poll_interval_seconds: Mapped[int | None] = mapped_column(Integer, nullable=True)
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), nullable=False, default=lambda: datetime.now(timezone.utc)
+    )